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| Length measurements using eyepiece reticles |
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As you have seen, eyepieces have been designed in such a way that the intermediate image of the microscope is located inside them. Therefore, so-called reticles can be attached which contain scales, grids, or comparison patterns. The reticles are made of thin glass plates on which scales are etched. These scales are aligned exactly with the intermediate image plane and then become visible in the microscope image.
If the size of an object in the specimen is to be determined, the eyepiece reticle is used as the comparison scale. The very precise scale divisions have a fixed spacing, for example 1/10 mm. To determine the size of an object, size D appearing in the intermediate image – here 7/10 mm – must be divided by the magnification of the objective. The magnification of the eyepiece, however, is of no relevance, since it only becomes effective after the intermediate image.
The result of the division is the object size d:
| d = D:M = 0.7mm:100 = 0.007mm = 7 µm |  |
M is the magnification of the objective used.
continue with: Calibration
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